sched/fair: Simplify post_init_entity_util_avg() by calling it with a…

… task_struct pointer argument

Since commit:

  d032669 ("sched/fair: Fix task group initialization")

the utilization of a sched entity representing a task group is no longer
initialized to any other value than 0. So post_init_entity_util_avg() is
only used for tasks, not for sched_entities.

Make this clear by calling it with a task_struct pointer argument which
also eliminates the entity_is_task(se) if condition in the fork path and
get rid of the stale comment in remove_entity_load_avg() accordingly.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Perret <quentin.perret@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20190122162501.12000-1-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -2433,7 +2433,7 @@ void wake_up_new_task(struct task_struct *p)
 #endif
 	rq = __task_rq_lock(p, &rf);
 	update_rq_clock(rq);
-	post_init_entity_util_avg(&p->se);
+	post_init_entity_util_avg(p);
 
 	activate_task(rq, p, ENQUEUE_NOCLOCK);
 	p->on_rq = TASK_ON_RQ_QUEUED;

kernel/sched/fair.c

@@ -759,8 +759,9 @@ static void attach_entity_cfs_rq(struct sched_entity *se);
  * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
  * if util_avg > util_avg_cap.
  */
-void post_init_entity_util_avg(struct sched_entity *se)
+void post_init_entity_util_avg(struct task_struct *p)
 {
+	struct sched_entity *se = &p->se;
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	struct sched_avg *sa = &se->avg;
 	long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
@@ -778,22 +779,19 @@ void post_init_entity_util_avg(struct sched_entity *se)
 		}
 	}
 
-	if (entity_is_task(se)) {
-		struct task_struct *p = task_of(se);
-		if (p->sched_class != &fair_sched_class) {
-			/*
-			 * For !fair tasks do:
-			 *
-			update_cfs_rq_load_avg(now, cfs_rq);
-			attach_entity_load_avg(cfs_rq, se, 0);
-			switched_from_fair(rq, p);
-			 *
-			 * such that the next switched_to_fair() has the
-			 * expected state.
-			 */
-			se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
-			return;
-		}
+	if (p->sched_class != &fair_sched_class) {
+		/*
+		 * For !fair tasks do:
+		 *
+		update_cfs_rq_load_avg(now, cfs_rq);
+		attach_entity_load_avg(cfs_rq, se, 0);
+		switched_from_fair(rq, p);
+		 *
+		 * such that the next switched_to_fair() has the
+		 * expected state.
+		 */
+		se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
+		return;
 	}
 
 	attach_entity_cfs_rq(se);
@@ -803,7 +801,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
 void init_entity_runnable_average(struct sched_entity *se)
 {
 }
-void post_init_entity_util_avg(struct sched_entity *se)
+void post_init_entity_util_avg(struct task_struct *p)
 {
 }
 static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
@@ -3590,10 +3588,6 @@ void remove_entity_load_avg(struct sched_entity *se)
 	 * tasks cannot exit without having gone through wake_up_new_task() ->
 	 * post_init_entity_util_avg() which will have added things to the
 	 * cfs_rq, so we can remove unconditionally.
-	 *
-	 * Similarly for groups, they will have passed through
-	 * post_init_entity_util_avg() before unregister_sched_fair_group()
-	 * calls this.
 	 */
 
 	sync_entity_load_avg(se);

kernel/sched/sched.h

@@ -1800,7 +1800,7 @@ extern void init_dl_rq_bw_ratio(struct dl_rq *dl_rq);
 unsigned long to_ratio(u64 period, u64 runtime);
 
 extern void init_entity_runnable_average(struct sched_entity *se);
-extern void post_init_entity_util_avg(struct sched_entity *se);
+extern void post_init_entity_util_avg(struct task_struct *p);
 
 #ifdef CONFIG_NO_HZ_FULL
 extern bool sched_can_stop_tick(struct rq *rq);